Are you well rested? You know sleep is the one thing we can’t cheat. We lose it in our busy lives and yet our brains, surprisingly keep score – and forces payback as soon as we lie down. And if it’s big, we sleep in – sometimes missing appointments, class, even parties.

But how does the brain keep track of sleep debt?

A clue has emerged from new research published in BioMed Central Neuroscience. Researchers have found that the expression of genes called “clock genes” are highly correlated with the need for sleep.

It’s proven that clock genes regulate our 24-hour circadian rhythm – but researchers say these genes also appear to control the amazing persistence of sleep.

Researchers studied mice that need a lot of sleep and those who need little sleep. They found that for all mice the expression of clock genes increased the longer an animal stayed awake, and decreased when the animal was in recovery sleep.

As for the purpose of sleep? No one knows. Scientists still argue whether it’s about restoring neuronal energy or consolidating our memories…. but since these clock genes are bound to energy metabolism, researchers may have given the restorative function of sleep a new boost.